The invention relates to a method and apparatus for use in packaging slices of a food product such as cheese slices, and more particularly to a linear stacker for stacking such slices in a form, fill and seal operation in a high speed commercial packaging line.
In packaging cheese slices or other stacked, sliced food products, the stacking operation may be a critical point in that it may represent a limiting factor in terms of throughput rate. Thus, there is a continuing need for improvements to increase the speed of existing stacking operations.
To be commercially viable, a method and apparatus for stacking slices in a high speed commercial operation must be very reliable, due to the fact that any interruption of the stacking operation may result in significant losses of time and material. If the stacking operation is interrupted, upstream production of the slices may also need to be interrupted, and slices that have already been formed and wrapped may be wasted.
The method and apparatus described below are useful in high speed commercial operations such as a continuous xe2x80x9chot packxe2x80x9d line wherein individually wrapped cheese slices are formed, separated, and stacked, and an overwrap is then formed, filled, and sealed around the stack, in a continuous, in line operation. In this type of process, the cheese slice may comprise a slice of pasteurized process cheese, pasteurized process cheese food, pasteurized process cheese spread, or the like, hot filled into a continuous wrapper to form a ribbon which is separated into individual wrapped slices. The method and apparatus of the invention may also be useful with other foods, such as slices of meat or natural cheese.
The invention provides a method and apparatus for stacking slices of food products such as wrapped cheese slices and the like at high speeds with high reliability. The apparatus comprises a vacuum conveyor for supporting slices from above, and at least one transfer bridge for mechanically peeling the slices sequentially from the conveyor and directing them downward into one or more stacking locations. The transfer bridge preferably comprises a plurality of downwardly sloping surfaces disposed beside the belts. The conveyor preferably comprises at least two parallel conveyor belts, each having a series of perforations therein communicating with a vacuum source. The transfer bridge preferably includes downwardly sloping surfaces disposed between the belts as well as outside the belts and extending below the elevation of the belts.
The transfer bridge may act on each particular slice while a vacuum is also acting on the same slice. To assist the transfer bridge in accelerating the slices downward, away from the belts, and to control slice position after separation, fluid pressure may be applied to the slices during and/or after separation of the slices from the belts by activation of one or more fluid actuators. Fluid pressure is preferably applied by directing a gas such as air at selected locations on the slice at selected times. A plurality of jets or nozzles may be employed to direct pulses of air at the selected portions of the slice at the selected times. Air may be supplied through a manifold 56 disposed downstream of a control valve.
The transfer bridge tends to tilt or rotate the slice while the slice proceeds forward. To counter the rotation applied by the transfer bridge, more fluid pressure is applied by the nozzles to the trailing portion of the slice. The fluid pressure may act on the slice to control its orientation and urge it downward into a stacking location before and/or after it has lost contact with the belts and transfer bridge.
To enable the pulses of air to be timed precisely in relation to the linear travel of the slice, the slice position is preferably detected by an optical sensor, a mechanical switch, or other means for sensing when the slice reaches a predetermined trigger point, traveling at a known velocity, and the pulses of air are activated at a predetermined time interval after the slice is detected at the trigger point. This time interval preferably takes into account the reaction time of the fluid actuator. To further increase the reliability of the apparatus, additional logic may be incorporated into the stacker control system to detect any slices that may adhere together. To avoid any interruption of stacking, the transfer bridge may then be disabled with respect to these joined slices. This ensures that a pair of overlapping slices will be directed to the same stacking location. Otherwise, the pair of slices might be draped over the wall between the stacking locations.
The method and apparatus may employ two or more conveyors operating in parallel. Each conveyor may have two or more stacking locations, and two or more transfer bridges associated therewith. One or more of the transfer bridges may be retractable to permit slices to travel past the retracted transfer bridge on the belt to reach stacking locations downstream therefrom. Stacks produced at a particular stacking location may be combined with those produced at other stacking locations from the same or other conveyors. In the preferred embodiment, the apparatus may attain an operating speed between approximately 100 and 2500 slices/minute. To improve efficiency and speed, the mechanical motions of the apparatus and the activation times of the fluid actuators are preferably parameterized in the control system to coordinate operation of the transfer bridges and fluid pulses.